The 3T3-L1 preadipocyte line is being used for the following purposes: (1) to analyze insulin and EGF receptor synthesis, turnover and function; (2) to establish the role of insulin in altering the state of cell protein phosphorylation and to purify insulin-regulated protein kinases and phosphoprotein phosphatases; (3) to investigate the hormonal regulation of triglyceride synthesis and breakdown by studying the biosynthesis and turnover of the principal enzymes involved; and (4) to develop cDNA probes for key lipid biosynthetic enzymes such as fatty acid synthetase and malic enzyme, in order to elucidate the mechanisms by which they are induced during the adipocyte conversion.